The present invention relates to rotary position sensors used to sense rotary movement using a sensor including a magnetosensitive device, such as a Hall effect device, and more particularly to a magnetic assembly therefor.
Rotary position sensors utilize a magnetic field and a magnetosensitive device, such as a Hall effect device or a magnetoresistor located within the magnetic field. To detect rotational movement as between a first article (such as for example a rotatable throttle shaft of an air control valve) and a second article (such as for example a stationary base), the magnetic field is oriented transverse in relation to the axis of rotation of the first article, and the magnetosensitive device is located inside the magnetic field. The member providing the magnetic field is connected to one of the articles, and the magnetosensitive device is connected to the other article. As the articles rotate relative to each other, the magnetosensitive device is caused to change its angular position relative to the magnetic field direction, resulting in a change of output signal from the magnetosensitive device responsive to its angle with respect to the magnetic field direction. This change in signal is indicative of the angular position as between the first and second articles.
FIGS. 1 and 2 depict a typical configuration of a prior art rotary position sensor 10. A shaft 12 supports a magnetic assembly 14 including two mutually opposed permanent magnet arcs 16, 18 and a keeper ring 20. A working air gap 22 is provided between the magnet arcs 16, 18, wherein a magnetic field B is provided therebetween having a direction D locally defined by the magnetic lines L. The magnet arcs 16, 18 are glued or bonded into place on the keeper ring 20. A magnetosensitive device 24 (as for example an AISC chip, such as a Melexis MLX90215 or Alegro ATS635LSB) is placed into the working air gap 22, and is connected to a base 26 by at least one peg 28. FIG. 3 depicts the magnetic field strength as a function of distance along the cross-section line 30. and indicates the magnetic field is nonuniform in that it drops in field strength on either side of the center of the working air gap.
What remains needed in the art is a magnet assembly for a rotary position sensor which is robust, yet simply constructed, and which provides a uniform magnetic field in the working air gap.
The present invention is a rotary position sensor featuring a robust and simply constructed magnetic field assembly which provides a uniform magnetic field in the working air gap for a conventional mangetosensitive device located thereinside.
The magnetic field assembly according to the present invention includes a plastic casing having a blind hollow, magnet pocket located at the blind end of the hollow, and a pair of diametrically opposed pole piece pockets oriented in upstanding relation to the magnet pocket. A permanent magnet is snapped into the magnet pocket, and a pole piece is respectively snapped into each of the pole piece pockets. The pole pieces may be rectangular or arc shaped, wherein the space therebetween forms the working air gap into which the magentosensitive device is placed. The magnetic field established in the working air gap is transverse to the axis of the blind hollow, and is generally uniform.
The aforesaid snapping feature is provided preferably by a plurality of nibs located at the periphery of the magnet and pole piece pockets which interferingly engage the respective magnet and pole pieces so as to retain them fixedly seated with respect thereto.
The casing may be configured to interface with either a stationary or rotatable article, as for example via a shaft cavity for being press-fit onto an end of a shaft.
Accordingly, it is an object of the present invention to provide a rotary position sensor including a simply constructed, snap together magnet assembly.
This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.